In semiconductor devices that include both transistor cells and a diode functionality such as RC-IGBTs (reverse conducting insulated gate bipolar transistors), mobile charge carriers flood a lightly doped semiconductor region along a forward biased pn junction and form a dense charge carrier plasma that results in a low forward resistance of the diode. When the forward bias at the pn junction changes to a reverse bias, a reverse recovery current relieves the charge carrier plasma thereby contributing to dynamic switching losses of the semiconductor device. During a desaturation period preceding the change from forward biased to reverse biased, a gated MOS (metal oxide semiconductor) channel may attenuate the charge carrier plasma in order to reduce the reverse recovery current and dynamic switching losses. A safety period between the end of the desaturation period and the change to reverse biased secures that the semiconductor device timely restores a blocking capability with closed MOS channel before commutation starts. During the safety period the charge carrier plasma may partially recover such that the safety period foils to some degree the effect of the desaturation period.
It is desirable to improve the switching characteristics of semiconductor devices that include both MOS gated channels and diode functionality.